This invention relates to generally to shock and vibration isolation for aircraft brake control valves, and more particularly relates to improved mounting of an electro-hydraulic brake control valve and a shock and vibration isolation system including shock and vibration isolators that can be used to isolate the mounting of the electro-hydraulic brake control valve from the undesirable effects of aircraft shock and vibration, and structural loads generated at the manifold mounting interface.
Conventional aircraft brake control valves are typically hard mounted by being bolted or otherwise rigidly secured by fasteners to a structural part or framework of the aircraft. However, some modern aircraft designs produce more severe random vibration environments than have been previously experienced that adversely affect the functioning of such hard mounted aircraft brake control valves. The problem is more acute with brake-by-wire aircraft brake control valves, because the brake control valves are typically operational for all braking functions, and are not just operational during a skid event.
For example, one type of brake control valve uses a pressure control valve with a flapper nozzle first stage that incorporates an armature that is essentially an undamped spring with a natural frequency in the 300 to 500 Hz range, depending on the armature spring rate. Vibration profiles at brake control valve mounting locations almost always contain this frequency, so that vibrations in this range will result in some degree of damage to the flapper nozzle as a result of motion of the undamped armature at its resonant frequency that can result in unsatisfactory performance or even failure of the brake control valves.
One known type of active/passive damping apparatus for large structures includes a passive type damping mechanism to be mounted on the structure, including an added mass, spring, and dampener. Hydraulic cylinders are mounted on the structure and connected to the added mass, with an electro-hydraulic servo mechanism to switch the hydraulic cylinders between passive and active type operation, and a control unit is provided for switching the electro-hydraulic servo mechanism between passive and active type operation in response to the velocity and displacement of the added mass as well as the velocity of the structure.
Another type of active vibration absorber is known for absorbing vibrations in a member that includes an inertial mass mounted on the member. A force actuator applies a force between the inertial mass and the member, and resonance of the active vibration absorber is damped. A first sensor provides a first signal indicative of at least one movement and/or stress related parameter for the member, and a second sensor provides a second signal indicative of a reaction of the inertial mass. A control unit is provided for controlling the force actuator arrangement using the first signal and the second signal.
A tuned mass damper is also known for damping dynamic response in a primary structure in one, two, or three dimensions. The tuned mass damper includes a secondary mass, a spring, and a viscoelastic element, with the spring and viscoelastic element interposed between the primary structure and the secondary mass.
A method is also known for stabilizing a nozzle flapper valve from oscillating, by adding an inertia tube to the flow path of the flapper valve nozzle, to effectively produce a stabilizing pressure force on the flapper at its natural frequency.
It would be desirable to provide a shock and vibration isolation mounting system for an aircraft brake control valve to allow the aircraft brake control valve to be mounted in environments that are often too severe for conventional hard mounted valve mounting arrangements. For example, it would be desirable to provide such a shock and vibration isolation mounting system to allow mounting of an aircraft brake control valve in a wheel well or near or on landing gear, due to their close proximity to brake pistons, allowing the use of shorter length hydraulic lines to provide faster system response and better system performance.
It also would be desirable to improve brake control valve reliability at conventional mounting locations where hard mounting of brake control valves has previously been used. It would also be desirable to provide a shock and vibration isolation mounting system that will allow the utilization of aircraft brake control valves having a less rigid valve structure as a result of lower stresses at the aircraft mounting interface, to provide weight savings in the mounting of brake control valves. In addition, it would be desirable to provide a shock and vibration isolation mounting system that will allow for brake control electronics that are typically isolated from shock and vibration to be co-located on shock and vibration isolated brake control valves to provide for improved signal processing and signal integrity due to close proximity of brake control electronics to a brake control valve and a wheel speed sensor. The present invention addresses these and other needs.